1. Field of the Invention
This invention relates to remote-control terminals for computers and, more particularly, to security devices which prevent unauthorized access to a digital computer by an illicit terminal.
Remote terminals for providing access to digital computers over digital information transmission paths, usually telephone lines, have been used for many years. A telephone number or other central switching number is used to select the particular circuit connected to the computer. Although steps have been taken in the past to maintain such a telephone number secret, the numbers are often discovered, and unauthorized access to the computer becomes a reality. Such access permits the computer to be used by unauthorized persons, often at a great expense to the legitimate operator. In addition, such use by unauthorized individuals renders the computer vulnerable to damage, both deliberate and accidental. A third deleterious result is the availability to outsiders of proprietary programs which are stored in the computer. Obviously, a system is required to prevent such unauthorized access.
2. Description of the Prior Art
As mentioned above, in the prior art the primary means used for preventing unauthorized access to a computer by illicit terminals has been maintaining the transmission path exchange number of the computer a secret. One of the primary disadvantages of this system has been the fact that such numbers are readily available to a large number of persons and are usually under the control of the organization providing the transmissiion path, not under the control of the computer operator.